As one of the two basic duplex modes, a Time Division Duplexing (TDD) mode has attracted more and more attentions due to an increasing demand on bandwidth for broadband mobile communication. In a TDD system, an identical frequency resource is used for both uplink and downlink transmission, and uplink/downlink signals are transmitted in different timeslots. In a public TDD system, e.g., a 3G-based Time Division-Synchronization Code Division Multiple Access (TD-SCDMA) system or a 4G-based TD-SCDMA Long Term Evolution (TD-LTE) system, the uplink and downlink timeslots are divided statically or semi-statically. Usually, during the network planning, a proportion of the uplink timeslot to the downlink timeslot is determined in accordance with a cell type and an approximate service ratio, and this proportion will remain unchanged. This method is simple and effective in the case that large coverage is provided by a macrocell. As specified in the 3rd Generation Partnership Project (3GPP) LTE Release 8/9/10, a frame structure in FIG. 1 is adopted in the TDD mode. There exist seven modes for uplink-downlink subframe allocation as shown in Table 1.
TABLE 1Modes for Uplink-Downlink Subframe AllocationUplink-Downlink-downlinkto-Uplinkconfig-Switch-pointSubframe numberurationperiodicity012345678905msDSUUUDSUUU15msDSUUDDSUUD25msDSUDDDSUDD310msDSUUUDDDDD410msDSUUDDDDDD510msDSUDDDDDDD65msDSUUUDSUUD
Along with the development of the technology, more and more low-power base stations, e.g., Pico cell and Home NodeB, have been deployed so as to provide small local coverage. In these microcells, there is relatively a small amount of terminals as well as a relatively large change in the requirement on terminal services. Hence, the requirement on the ratio of the uplink service to the downlink service for these cells may be dynamically changed. Although the TD-LTE standard, for example, also supports to change online the proportion of uplink timeslot to the downlink timeslot of the cell, a complex signaling procedure and additional configuration time are required, so the system performance will be degraded and it is impossible to track the service change in real time.
Based on the above, a Rel-11 research project “Further Enhancements to LTE TDD for DL-UL Interference Management and Traffic Adaptation” (3GPP TR36.828) has been launched by the 3GPP, so as to study the ways for the flexible change of UpLink-DownLink (UL-DL) subframe allocation in the microcells in accordance with the service requirements. One of the ways includes transmitting, by a base station, information about the TDD UL-DL subframe configuration to a terminal using a channel and/or signal at a physical layer. This way may support the change of the UL-DL subframe allocation in a radio frame once per 10 ms. A typical physical layer signaling method includes indicating the information about the TDD UL-DL subframe configuration using a Downlink Control Indicator (DCI), especially using an existing DCI format.
The DCI is mainly carried by a Physical Downlink Control Channel (PDCCH) so as to effectively transmit uplink/downlink scheduling information and the relevant public control information. Currently, 10 DCI formats have been defined in an LTE system, and their principal functions are shown in Table 2.
TABLE 2Functions of 10 DCI FormatsDCI FormatFunction0Used for Scheduling UL transmission on the PUSCH1Used for Scheduling transmission of one codeword on the PDSCH1AUsed for compact Scheduling of one codeword on the PDSCH1BUsed for compact Scheduling of one codeword on the PDSCHwith precoding information1CUsed for very compact Scheduling of one codeword on thePDSCH1DUsed for compact Scheduling of one codeword on the PDSCHwith precoding information and power offset information2Used for Scheduling of two codewords on the PDSCH withclosed-loop spatial multiplexing2AUsed for Scheduling of two codewords on the PDSCH withopen-loop spatial multiplexing3Used for Transmitting power control information for PUCCH andPUSCH with 2-bit indicator for a group of users3AUsed for Transmitting power control information for PUCCH andPUSCH with 1-hit indicator for a group of users
The DCI message bit is checked by a Cyclic Redundancy Check (CRC) and added with CRC information. Its CRC information bit is scrambled with a Radio Network Temporary Identifier (RNTI), and then channel coding and rate matching are performed.
Depending on their functions, the DCI formats may be further divided into four principal types, including DCI format for scheduling Physical Uplink Shared Channel (PUSCH), e.g., DCI format 0, DCI formats for scheduling Physical Downlink Shared Channel (PDSCH), e.g., DCI formats 1, 1A, 1B, 1D, 2 and 2A; DCI formats for scheduling public control information, e.g., DCI formats 1A and 1C; and DCI formats for scheduling multicast power control information, e.g., DCI formats 3 and 3A.
As an optimum detection algorithm, maximum likelihood detection algorithm may be used to completely acquire reception diversity gains. However, this algorithm is too complex, and during the detection, it is required to traverse all possible transmission vectors. When the DCI message having a length of NL and coded with an M-base system is to be transmitted, it is required to traverse all the MNL dedicated symbol vectors in the space. Taking the DCI format 1C (20M) with the least bits as an example, when M=2 and NL=15, MNL=32768. The resultant volume of search queries is unacceptable in an actual system. Hence, the maximum likelihood detection algorithm may be applicable only when there are few valid bits.
Basic Principle of Carrier Aggregation
An LTE R8 carrier is used as a basic unit, each LTE R8 carrier constitutes a Component Carrier (CC), and a plurality of CCs is aggregated to provide a greater bandwidth. Each carrier has a maximum bandwidth of 20 MHz. This multi-carrier mode is called as a carrier aggregation mode. As shown in FIG. 2, five CCs each having a bandwidth of 20 MHz are aggregated to provide a bandwidth of 100 MHz.
There are two ways for the carrier aggregation. One of the ways includes the aggregation of a plurality of continuous carriers within a band, and in order to facilitate the operator's flexible use of spectra, it also supports the aggregation of a plurality of discontinuous spectra. For the continuous carrier aggregation, all the CCs belong to an identical band, and for the discontinuous carrier aggregation, the aggregated CCs may be located within an identical band or different bands. As shown in FIG. 3, which is a schematic view of the discontinuous carriers, the two cross-band CCs each having a bandwidth of 20 MHz are aggregated into a multi-carrier system having a bandwidth of 40 MHz.
Scenarios for Coordinated Multi-Point Operation
Scenario 1: intra-site coordination in a homogenous network, as shown in FIG. 4a. 
Scenario 2: coordination of multiple transmission nodes in a homogeneous network (intra-eNB), as shown in FIG. 4b. 
Scenario 3: coordination of multiple transmission nodes in a heterogeneous network, where multiple low-power nodes are deployed within the coverage of a macro base station, and a separate cell identifier (ID) is configured for each transmission node, as shown in FIG. 4c. 
Scenario 4: coordination of multiple transmission nodes in a heterogeneous network, where multiple low-power nodes are deployed within the coverage of a macro base station, and an identical cell ID is configured for all the transmission nodes, as shown in FIG. 4c Scenario 4 differs from Scenario 3 essentially in that the identical cell ID is configured for all the transmission nodes, and uniform cell-level public information (e.g., a public DCI message) is transmitted via the transmission nodes. As shown in FIG. 4d, the uplink/downlink configuration information may be separately configured for each transmission node, and the identical public DCI message is transmitted via all the transmission nodes.
It can therefore be seen that, in spite of various uplink/downlink configuration, there is no method for indicating the TDD uplink/downlink configuration information.